Self-indicating tensioner for a belt scraper

ABSTRACT

A self-indicating tensioning device for a scraper blade includes a flat spring coupled at one end to a rotatable shaft which supports the blade and coupled at it&#39;s other end to an adjusting mechanism. The adjusting mechanism is operable to exert a force on the flat spring which in turn applies a torque to the rotatable shaft for displacing the scraper blade. An indicator rod has one end fixed to the rotatable shaft and the other end is free and located adjacent to a graduated indicator plate.

This application claims the benefit of U.S. Provisional Application No.60/032,272, filed Dec. 2, 1996.

FIELD OF THE INVENTION

The present invention relates to a tensioning device for adjusting theforce with which the blade of a conveyor belt scraper contacts theconveyor belt surface, and in particular, to such a device whichprovides an indication of the amount of force being applied by thetensioning device.

BACKGROUND OF THE INVENTION

A conveyor belt typically includes one or more scraper assemblies thatare constructed and disposed along the belt for removing remnants ofmaterials carried by the conveyor belt that adhere to the belt surface.A scraper assembly often includes one or more scraper blades arrangedacross the width of the conveyor belt. The blades are mounted on asupport arm or arms that are affixed to and extend from a transverselymounted, rotatable support shaft. Rotation of the transverse supportshaft moves the scraper blade or blades into and out of contact with thebelt surface.

The cleaning efficiency of the scraper assembly depends on the magnitudeof the force exerted by the scraper blade against the belt surface. Ifthe contacting force is too great, the scraper blade will wearprematurely. On the other hand, if the contacting force is too low, theblade will not clean the belt efficiently. Torsional coil springs,torsion rod springs, air cylinders, hydraulic cylinders, and similardevices are used to adjust the force with which a scraper blade contactsa conveyor belt surface. In pneumatic and hydraulic systems a pressuregage provides an indication that can be correlated with the amount offorce being applied. It would be highly desirable to have a tensioningdevice for a belt scraper assembly that provides an instantaneousindication that can be easily used to reproducibly set the amount offorce with which the scraper blade contacts the belt surface.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided aself-indicating tensioning device for adjusting the contacting force ofa scraper blade against the surface of an endless conveyor belt. Theself-indicating tensioning device according to this invention has arotatable shaft which supports the scraper blade such that rotation ofthe rotatable shaft displaces the scraper blade vertically. A flatspring is coupled at one end to the rotatable shaft and at the other endto an adjusting mechanism. The adjusting mechanism exerts a force on theflat spring which thereby applies a torque to the rotatable shaft. Theend coupled to the adjusting device is movable relative to the endaffixed to the rotatable shaft. An indicator rod extends radially fromthe rotatable shaft with one end fixed to the rotatable shaft and theother end is free such that the force exerted on the flat spring doesnot cause deflection of the indicator rod. A graduated indicator plateis attached to the movable end of the flat spring and is movablerelative to the indicator rod. As the flat spring deflects in responseto the application of force thereto, the displacement of the graduatedindicator plate relative to the free end of the indicator rod providesan indication of the amount of force exerted on the flat spring, theamount of torque applied to the rotatable shaft, or the amount of forcewith which the scraper blade contacts the conveyor belt.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary of the present invention, as well as the followingdescription of a preferred embodiment thereof, will be better understoodby referring to the drawings, wherein:

FIG. 1 is a perspective view showing a portion of a conveyor belt and ascraper assembly used in connection therewith in accordance with thepresent invention;

FIG. 2 is a perspective view showing a tensioning device in accordancewith the present invention for use with the scraper assembly shown inFIG. 1;

FIG. 3 is an elevational view of a spring and indicator subassembly ofthe tensioning device shown in FIG. 2 when the torque applying mechanismis in the neutral position; and

FIG. 4 is an elevational view of the spring and indicator subassembly ofthe tensioning device shown in FIG. 3, showing how the leaf spring isdisplaced when force is applied thereto.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a portion of a conveyor belt 10which travels in a direction indicated by the arrow A. A belt cleaningassembly 12 is disposed adjacent to the belt 10. The belt cleaningassembly 12 includes a scraper assembly 14 and a tensioning assembly 16mechanically linked to the scraper assembly 14. The scraper assembly 14includes a scraper blade 17 that is positioned under and maintained incontact with the conveyor belt 10 for cleaning off remnants of thematerial being carried by the conveyor belt 10. The scraper blade 17 ismounted on a blade support bar 18 which spans the width of the conveyorbelt 10. The ends of blade support bar 18 engage with receptacles oropenings in the blade ends of a pair of pivot arms which link the bladesupport bar to a rotatable cross shaft 20 that also spans the width ofthe conveyor belt 10 in parallel relation to the blade support bar 18.The rotatable cross shaft 20 has a generally polygonal, preferablysquare, cross section. For clarity, only the near side pivot arm 21, itsblade end 22, and its cross-shaft end 23 are shown in FIG. 1. Thecross-shaft end 23 of pivot arm 21 is formed to engage with cross shaft20 such that it can rotate therewith. To that end the cross-shaft endsof the pivot arms include polygonal shaped openings therethrough. In theembodiment shown in FIG. 1, cross-shaft end 23 has a square openingtherein for receiving the square cross shaft 20.

An extension 24 extends from the near end of cross shaft 20 and througha support bracket 26 that is mounted to the support frame of theconveyor belt 10. A similar arrangement (not shown) is provided on thefar end of cross shaft 20. The extensions have polygonal cross sectionsthat match that of cross shaft 20 although smaller in dimension. Aconnector block 28 is mounted on the outboard end of extension 24 sothat it can be rotated therewith. In the embodiment shown in FIG. 3,connector block 28 has a square opening therein for receiving the squareextension shaft 24. Extending from one side of connector block 28 is aflat or leaf spring 30 and an indicator rod 32 which are fastened to abracket 34 on connector block 28. An indicator plate 36 is affixed tothe end of the flat spring 30 that is distal from the connector block28. Indicator plate 36 has a plurality of graduations formed thereon.The free end of indicator rod 32 is positioned adjacent to the indicatorplate 36.

The flat spring 30 is preferably machined from flat stock of a springsteel. Because conveyor belts of different widths require differentamounts of scraper blade force for effective cleaning, the force appliedto the flat spring 30 will depend on the width of the belt with which itis used. The thickness of the spring steel flat stock is selected basedon the amount of force that will be exerted on the spring 30 and themaximum amount of deflection that can be tolerated for the spring 30when stressed. To accommodate the use of various thicknesses of springs,the bracket 34 has a fixed space 37 which is dimensioned to receive aspring having the maximum desired thickness. When springs of smallerthickness are used, one or more shims are employed to fill out thebracket space and ensure a tight fit. The flat spring 30 and anynecessary shim(s) are secured to the bracket 34 with a suitablefastener, preferably a bolt and nut assembly 39.

The tensioning assembly 16 is connected between a fixed structure 23,such as the conveyor support frame, and the movable end of spring 30.The tensioning assembly 16 operates to displace the movable end ofspring 30, thereby imparting torque to pivot the cross shaft 20 to raisescraper blade 17 into engagement with the conveyor belt 10 or to lowerit into disengagement therefrom.

Referring now to FIG. 2, a mounting bracket 38 is attached to aconvenient fixed structure such as the conveyor support frame. An anchorclevis 40 is attached to the mounting bracket 38. An anchor rod 42 iscoupled to the anchor clevis 40 with a bolt and nut assembly 44. Theanchor rod 42 has a threaded end 45 that is threaded into one end 46a ofa barrel 48 that is part of a force actuator 50. A drive rod 52 has athreaded end 54 that is threaded into the opposite end 46b of barrel 48.The non-threaded end of drive rod 52 is coupled to a drive clevis 56with a bolt and nut assembly 58. The drive clevis 56 is fastened to theend of the flat spring 30 by any suitable means.

The force actuator 50 includes a handle 60 and ratchet mechanism 62 forrotating the barrel 48. The thread on threaded end 45 of anchor rod 42is counter to that on threaded end 54 of drive rod 52. Therefore, whenthe force actuator barrel 48 is rotated, the drive rod 52 moves towardor away from anchor rod 42 depending on the direction of rotation of theforce actuator barrel 48. As the force actuator barrel 48 is rotated,either a pulling or a pushing force is applied to the end of spring 30through drive clevis 56. The force thus applied to the end of spring 30causes a torque to be applied to connector block 28, and in turn tocross shaft 20. That torque causes cross shaft 20 to rotate therebybringing scraper blade into engagement with or disengagement fromconveyor belt 10. As greater force is applied to spring 30, more torquewill be applied to cross shaft 20, thereby causing scraper blade 17 tocontact the conveyor belt 10 with proportionally greater force.

However, when scraper blade 17 is in contact with belt 10, cross shaft20, which is formed of a rigid material such as steel, will resist thetorque applied to it through connector block 28. Consequently, themovable end of spring 30 will deflect in the direction of the forceapplied to it as shown in FIG. 4. The indicator rod 32 attached toconnector block 28 will not deflect as force is applied to the spring30. The indicator plate 36 affixed to spring 30 will move relative tothe free end of indicator rod 32 as the end of spring 30 deflects. Thegraduation that is then adjacent to the free end of indicator rod 32provides an indication of the amount of torque that is being applied toconnector block 28 and cross shaft 20. The graduations on indicatorplate 36 can be calibrated to provide an indication of the amount offorce with which the scraper blade 17 contacts the belt surface.Alternatively, the graduations on indicator plate can be calibrated toindicate the amount of torque applied to the rotatable shaft or theamount of force with which the scraper blade contacts the conveyor belt.It will be appreciated that the arrangement described provides asignificant advantage in providing the ability to set and reproduciblyreset the scraper blade force by simply operating the force actuator 30until the desired graduation on indicator plate 36 is adjacent the endof indicator rod 32.

It will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concept of the invention. It shouldtherefore be understood that this invention is not limited to theparticular embodiments described herein but is intended to include allchanges and modifications that are within the scope and spirit of theinvention as set forth in the following claims.

What is claimed is:
 1. A self-indicating tensioning device for adjustingthe contacting force of a scraper blade against the surface of anendless conveyor belt, the tensioning device comprising:a rotatableshaft which supports the scraper blade such that rotation of saidrotatable shaft results in displacement of the scraper blade toward oraway from the belt; an elongated flat spring coupled at one end to saidrotatable shaft; an adjusting mechanism coupled to a second end of saidflat spring distal from said rotatable shaft for displacing the secondend of said flat spring; an indicator rod extending radially from saidrotatable shaft and having one end fixed to said rotatable shaft and theother end free; an indicator plate affixed to the second end of saidflat spring; said flat spring being adapted to deflect in response tothe application of force by said adjusting device and cause displacementof said graduated indicator plate relative to the free end of saidindicator rod.
 2. The tensioning device as recited in claim 1, whereinsaid indicator device comprises a pointer.
 3. The tensioning device asrecited in claim 1, wherein said adjusting device comprises a turnbucklewith two counter-threaded links, one of said links being coupled to aconveyor support structure and the other end being connected to saidflat spring.
 4. The tensioning device as recited in claim 3, whereinsaid turnbuckle comprises a ratchet for rotating said counter-threadedlinks.
 5. The tensioning device as recited in claim 1, wherein the fixedend of said indicator rod is disposed adjacent to the point ofattachment of said elongated flat spring to said rotatable shaft.